The iPhone 4S also scored more first-day pre-orders than any other Apple product

Earlier this month, Apple introduced the successor to the iPhone 4: the iPhone 4S. Now, reports are saying that the newest addition to the iPhone family has sold out for pre-order at all three U.S. carriers.

Initially, customers and investors were disappointed at the announcement of the iPhone 4S. They spent a good portion of 2011 anticipating a revolutionary iPhone 5 product, but instead, received an iPhone 4S with few external changes. However, the 4S does offer new internal changes such as a dual-core A5 processor, the new iOS 5 mobile operating system, an 8-megapixel camera with backside illumination and compatibility across CDMA and GSM networks.

When it came time for the iPhone 4S pre-order, which became available October 7, customer disappointment was anything but evident. Within the first 24 hours of pre-order availability, Apple hit one million 4S pre-orders, which is the most first-day pre-orders any Apple product has ever achieved according to Philip Schiller, Apple's senior vice president of Worldwide Product Marketing.

Now, any sign of disappointment has gone straight out the window because Apple's iPhone 4S has sold out for pre-order in the U.S. at AT&T, Verizon and Sprint.

"It looks like another blockbuster launch for Apple, only this time with three carriers," said Roger Entner, an analyst with Recon Analytics LLC.

While factors such as the addition of Sprint as a carrier along with its unlimited plans has helped spark iPhone-mania, Tero Kuittinen, an independent wireless industry analyst, says that this particular iPhone model got an extra boost from former Apple CEO Steve Jobs' recent passing on October 5.

According to Kuittinen, customers are looking to obtain a piece of history, as the 4S is the last iPhone to be designed under Jobs as CEO. Others are likely just upgrading from expired contracts with the iPhone 3GS. Kuittinen added that this excitement for the 4S early on may be "an inaccurate indication of longer-term demand."

In addition to popular iPhone demand, a comScore study recently found that iPads are killing the competition with 97.2 percent of U.S. tablet traffic in August 2011.